Arsenic Acid is useful in preparing wood preservatives. It is prepared commercially by the nitric acid or hydrogen peroxide oxidation of arsenous acid. In the nitric acid process, a stoichiometric amount of nitric acid is used. A plant is required to manufacture nitric acid from the oxides of nitrogen which are produced when arsenous acid is oxidized and the oxides of nitrogen cause a pollution problem when the gas is vented to the atmosphere. Evdokimov, Zhurnal Prikladnoi Khimii, Vol. 34, No. 5, pp. 1152-1154, describes the oxidation of arsenous compounds by nitric acid with atmospheric oxygen and a iodine catalyst at a concentration of 600 to 1000 ppm.
It is also reported that arsenous compounds can be oxidized by atmospheric oxygen with nitrogen oxides, nitric acid, and iodine on activated charcoal. Evodokimov, Zhurmal Prikladnoi Khimii, Vol. 33, No. 11, pp. 2435-2439.
The prior art processes suffer one or more disadvantages such as requiring either a stoichiometric amount of nitric acid, relatively large amounts of halide catalyst (e.g. 600-1000 ppm), high concentrations of nitric acid (e.g. 25%), consumption of 25% or more of the nitric acid, and high temperatures and pressures of 200.degree.-300.degree. C. and 60-80 atm.
Hydrogen peroxide, although non-polluting, is a very expensive oxidant.
Thus a need exists for an inexpensive non-polluting process for the production of arsenic acid which has now been discovered.